Teens and young adults who regularly smoke pot can suffer from loss of attention, poor memory and decreased IQ, according to psychologists at the American Psychological Association.

“It needs to be emphasized that regular cannabis use, which we consider once a week, is not safe and may result in addiction and neurocognitive damage, especially in youth,” Krista Lisdahl, director of the brain imaging and neuropsychology lab at University of Wisconsin-Milwaukee, said at the APA’s annual convention in Washington, D.C. Saturday.

Lisdahl said young people who become addicted to marijuana lose about six IQ points by the time they reach adulthood, and brain imaging suggests significant changes to the structure of the brains of regular users, most prominently among adolescents.

Psychologists discussed the possible public health impact of marijuana legalization, which is only likely to ramp up following successful ballot measures in 2012 that legalized the drug for adult recreational use in Washington and Colorado. Alaska and Oregon, as well as the District of Columbia, are set to vote on the question this fall.

Legalization advocates, of course, say that bringing pot into a regulated marketplace will actually help keep it away from minors and that prohibition not only benefits criminals but also makes it easier for young people to acquire the drug.

That’s the argument forwarded in Canada by Liberal leader Justin Trudeau, who has vowed to “tax and regulate” pot sales if his party forms government in 2015. The NDP favours decriminalization, which would remove criminal sanctions without legalizing sale, while the Conservative Party insists cannabis is a harmful substance that should remain illegal.

According to a government-commissioned poll from early 2014, more than two thirds of Canadians want the nation’s drug laws loosened but only 37 per cent think marijuana should be legalized outright. About 33 per cent said possession of small amounts of pot should merit only a fine, while another 25 per cent want punishment for marijuana possession to stay the same or increase.

According to Lisdahl, presenting to the APA, marijuana use is increasing among youth in the States. She cited a 2012 study that showed daily pot use among high school seniors had more than doubled from the 1990s, from 2.4 per cent to 6.5 per cent.

Health Canada estimates that almost 40 per cent of Canadians try pot in their lifetimes, and the average age at which people are introduced to the drug is 15.